I'm using the CC1120. Works great on our RF project. I have recently added a SD card on the SPI bus, which is causing some quirkiness with the RF chip. I have the RF chip using SPI mode 0. I think I remember way back that mode 0 was the preferred mode. Not sure whether that is correct or if mode 3 can also be used. However, what I am seeing is that if I use the SD card (also in Mode 0), then for about 20 seconds or so after an SD transaction and subsequent CS back high, MISO still gets held high and prevents the RF chip from accessing the bus. After 20 seconds, the bus is released and things work OK. I am using "while (SO != 0)" to wait for a low bus, which was used in the demo code for the CC1120. I've never used a 'wait for low SO' procedure before in any SPI peripheral I've ever used before, so not sure if this is just recommended for this group of RF chips or not. SD cards should be able to use mode 0 or 3.
I'm not sure why the SD card is holding the bus, but when I use Mode 0 for RF and Mode 3 for the SD card, or Mode 3 for both, everything works fine and no bus delay. But, I'm not sure if Mode 3 is a good mode for the CC1120. This only happens after doing an SD transaction and CS is raised back high again.
So, first things first, can the CC1120 be used in both SPI modes 0 and 3?
Also, I have 10K pullups on the SI and SO lines.